The Yankee slugger’s retirement plan includes becoming an underwear mogul, Page Six has learned.

The slugger is a secret owner of Frigo RevolutionWear — a customized men’s underwear brand that sells skivvies more colloquially known as “Tempur-Pedic banana hammocks.” The high-tech undies sell for $100 a pair and include a “soft lock adjustment system” plus a “patented pouch” dubbed the “Frigo Zone.” (We’ll leave the zone’s location to your imagination.)

Jeter has endorsed the expensive unmentionables in the past, but his reps have been trying to keep it under wraps that he’s an investor in the top-shelf drawers, too.

“His team is concerned he’ll turn into the next Jim Palmer,” said a source, referencing the Hall of Fame pitcher who became the face, and more, of Jockey International and appeared in print and TV ads — and on Times Square billboards — in tight bikini briefs of every stripe in the 1970s.

But Jeter is unlikely to appear in any ads. He told us himself last year at a bash for a Frigo pop-up store, “It’d be too embarrassing.” He claimed he was attending the event because he’s pals with Frigo CEO Mathias Ingvarsson, who we’re now told has around the same stake in the company as the Yankee captain.

Ingvarsson has previously explained of the undergarments: “It separates your genitals from the rest of your body . . . It lifts a little bit so [guys] feel the comfort.”

The product’s marketing materials further explain: “Unlike other garments that keep things in place by compressing your package inward, Frigo provides support from behind so you won’t feel constricted.” All right, then!

Jeter has been spotted wearing Frigo-branded outerwear, and has offered his endorsement without disclosing his ownership stake.

Along with the Bronx Bomber, other celebs with stakes in Frigo include Knicks star Carmelo Anthony and entrepreneurial rapper 50 Cent.